On Tuesday, November 21, 2017 at 10:53:39 PM UTC-7, John B. wrote:
I'm rebuilding a rear (derailier) wheel as, to be frank, I used spokes
that were slightly smaller in diameter on the cassette side of the
wheel then probably wise, and had occasional spoke breakage. I finally
got some slightly larger diameter spokes and am lacing the cassette
side of the wheel.

Over probably a couple of years I had four spokes break, one at a
time, all were what Sheldon referred to as trailing spokes, the ones
that have the highest strain when pedaling, and all broke at the
middle of the bend at the head end.

While I was lacing the wheel with the new spokes I got to wondering
whether the side of the hub flange that spoke heads were on might have
had any effect on strength.

I have always laced 36 hole wheels over three for rear wheels and over
two for front wheels with the trailing spoke heads on the outside of
the hub flange and the leading spokes with the heads on the inside of
the flange, as I believe that Sheldon recommended.

But I also remember someone here with a rant about rear wheel lacing
who I think was recommending that on the cassette side that the heads
should all be toward the outside of the flange. I assumes to prevent
damaging spokes if the chain were to come off the largest cassette cog
and jam between the spokes and the cassette.

This is the only wheel I've had problems with and I deliberately
bought the bits and pieces with the idea of long life in mind -
cartridge wheel bearings and medium weight rim with eyelets, etc., and
as this is the only wheel that I've had problems with I'm fairly sure
that my wheel building technique is reasonably effective.

Any thoughts on spoke head orientation and the effect on spoke
strength.

--
Cheers,

John B.

need to examine each spoke for cracks with a magnifier. Generic spokes are for very casual no load riders.